The present invention relates to a process for coating powder particle substrates, the coated powder particle substrates and to applications and uses thereof. More particularly, the invention relates to coating powder particle substrates with a metal oxyanion containing material, such material preferably being an electrically and/or thermally conductive oxyanion containing material and such coated powder substrates.
In many applications using powder it would be advantageous to have an electrically and/or thermally conductive; radiation absorbing and/or improved mechanical oxyanion coatings which are substantially uniform, have high and/or designed conductivity and/or radiation absorbing properties and/or improved mechanical properties and have good chemical properties, e.g., morphology, stability, corrosion resistance, etc.
A number of techniques have been employed to provide certain metal oxyanion coatings on fixed generally larger size substrates. For example, the CVD processes are well known in the art for coating a single flat surface, which is maintained in a fixed position during the contacting step. The conventional CVD process is an example of a xe2x80x9cline-of-sightxe2x80x9d process or a xe2x80x9ctwo dimensionalxe2x80x9d process in which the metal oxyanion is formed only on that portion of the substrate directly in the path of the metal source as metal oxyanion is formed on the substrate. Portions of the substrate, particularly internal and external surfaces, which are shielded from the metal oxyanion being formed, e.g., such as the opposite side and edges of the substrate which extend inwardly from the external surface and substrate layers which are internal or at least partially shielded from the depositing metal oxyanion source by one or more other layers or surfaces closer to the external substrate surface being coated, do not get uniformly coated, if at all, in a xe2x80x9cline-of-sightxe2x80x9d process. Such shielded substrate portions either are not being contacted by the metal source during line-of-sight processing or are being contacted, if at all, not uniformly by the metal source during line-of-sight processing. A particular problem with xe2x80x9cline-of-sightxe2x80x9d processes is the need to maintain a fixed distance between the source and the substrate. Otherwise, metal oxyanion can be deposited or formed off the substrate and lost, with a corresponding loss in process and reagent efficiency.
There has been a need to develop processes for producing metal oxyanion coated powder substrate particles and processes, particularly under fast reaction processing conditions, which provide short processing times required for producing high quantities of metal oxyanion coated powder particle substrates and to produce unique metal oxyanion coated powder substrates having improved properties
A new process, e.g., a xe2x80x9cnon-line-of-sightxe2x80x9d or xe2x80x9cthree dimensionalxe2x80x9d process, useful for coating of three dimensional powder particle substrates has been discovered. As used herein, a xe2x80x9cnon-line-of-sightxe2x80x9d or xe2x80x9cthree dimensionalxe2x80x9d process is a process which coats surfaces of a powder substrate with a metal oxyanion coating which surfaces would not be directly exposed to metal oxyanion forming compounds being deposited on the external surface of the substrate during the first line-of-sight contacting step. In other words, a xe2x80x9cthree dimensionalxe2x80x9d process coats coatable powder substrate surfaces which are at least partially shielded by other portions of the powder substrate which are closer to the external surface of the powder substrate and/or which are further from the metal oxyanion forming source during processing, e.g., the internal and/or opposite side surfaces of for example glass, ceramic or mineral powder particle substrates such as fibers, spheres, flakes or other shapes or surfaces including porous shapes.
A new fast reaction, elevated temperature process for coating a three dimensional powder substrate having shielded surfaces with a metal oxyanion, preferably a conductive or radiation absorbing or mechanically improved metal oxyanion coating on at least a part of all three dimensions thereof and on at least a part of said shielded surfaces thereof has been discovered. In brief, the process comprises forming a reaction mixture comprising powder substrate particles, a metal oxyanion precursor, for example, silicon, aluminum, boron, zirconium, lanthanum and titanium precursors, such as oxide, partial oxide and chloride containing precursors, an anion forming precursor said metal and the anion of said precursors being chemically different and an oxy precursor chemically the same or different than one or both of said metal oxyanion and anion forming precursor and reacting the reactant mixture under fast reaction short residence time, high temperature conditions in a reaction zone to form a metal oxyanion coated substrate and recovering such coated substrate, preferably a conductive or radiation absorbing or mechanically improved oxyanion containing coated substrate.
The anion forming precursor is typically a precursor agent that provides the anion portion of the metal such as boron, nitrogen, silicon, carbon and sulfur. The anion forming precursors can be in the form of a gas, liquid or solid for example methane and carbon powder as a source for carbon, nitrogen and ammonia as a source for nitrogen, boron halides such as boron trichloride as a source for boron, sulfur halides and hydrogen sulfide as a source for sulfur and various silicon halides and hydrosilicides as a source for silica.
The forming of the metal oxyanion precursor/substrate, the oxy precursor and anion forming precursor reactant mixture preferably takes place closely in time to reacting in the reaction zone. In a particularly preferred embodiment, the reaction mixture after formation is introduced directly into the high temperature reaction zone under fast reaction processing reducing conditions. The coated powder substrate is then recovered by conventional means.
The process can provide unique coated substrates including single and mixed oxyanions which have application designed conductivity and/or absorbing properties and/or improved mechanical properties so as to be suitable for use as components such as additives in a wide variety of applications. Substantial coating uniformity, e.g., in the thickness of the metal oxyanion coating is obtained. Further, the present metal oxyanion coated substrates in general have outstanding stability, e.g., in terms of electrical, thermal and mechanical properties and morphology and are thus useful in various applications.